Bring code up to modern standards

Build with mkdocs instead of sphinx (#143)

Moved `quaternion` to `src/quaternion` to work around bad behavior by RTD

Moved `test` directory to more standard `tests`

Simplified versioning with post-commit amending hook

Bring code up to modern standards

Bring code up to modern standards (#142)

  * Reorganize code into subdirectories
  * Remove old disused CI stuff
  * Add Github Actions integration
  * Add pyproject.toml
  * With pyproject, pep 517/8 simplifies the setup file dramatically

Tested and releasable

v2.0

Re-add numba wrapper that was mistakenly removed